1. Field of the Invention
The present invention relates to a method of producing a GaN independent substrate, a method of producing a GaN crystal body, and a method of producing a GaN substrate.
2. Related Background Art
Document 1 (Japanese Patent Application Laid-Open No. 2000-12900) describes a GaN single-crystal substrate. A mask having zigzag windows or stripe windows is formed on a GaAs (111) substrate, a GaN buffer layer is formed at low temperature by HVPE or by MOC, a thick GaN epitaxial layer is grown at high temperature by HVPE, and the GaAs substrate is then removed. By using the self-sustained films of GaN as seed crystals, a thick GaN is grown by HVPE to form a GaN ingot. This ingot is sliced with a slicer to obtain a transparent and colorless GaN wafer with little warp.
Document 2 (Japanese Patent Application Laid-Open No. 2002-284600) describes a method of producing a GaN crystal substrate, and a GaN crystal substrate. A metal film is deposited on a starting base which is one of the following: a single-crystal sapphire substrate; a substrate obtained by growing a single-crystal GaN film on a sapphire substrate; and a single-crystal semiconductor crystal substrate. A GaN film is then deposited on the metal film to form a laminated substrate, which facilitates separation of the grown GaN film and the starting base.
Document 3 (Japanese Patent Application Laid-Open No. 2003-168820) describes a method of separating a crystal layer formed on a substrate by exposing the crystal layer and the substrate to light. This separation method is characterized by irradiating the layer with a line pattern of light. At this time, the irradiation width with the light is approximately equal to or smaller than the thickness of the crystal layer, whereby the crystal layer can be separated from the substrate, without occurrence of crack.